Semiconductor laser device and heat sink used therein

ABSTRACT

A semiconductor laser device has a heat sink of which laminated plural plates are constituted and a semiconductor laser element mounted on upper surface of the heat sink. The heat sink has a channel in which a coolant flows inside thereof. The heat sink includes a channel-forming plate portion that forms the channel and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel. The mounting plate portion is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser element than that of the channel-forming plate portion.

The present invention contains subject matter related to Japanese Patent Application No. JP2005-115118 filed in the Japanese Patent Office on Apr. 12, 2005, the entire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor laser device and a heat sink used therein.

2. Description of Related Art

A semiconductor laser device in a range from several watts to a few tens watts has often used a water-cooled system therein in order to implement high-power and high-reliability. Heat sink of micro channel type is well known as a heat sink structure to implement high heat-removing efficiency.

As a method of forming a fine interior channel structure such as micro channel typed one, a method of laminating metal thin plates in which a pattern is etched by etching or the like and bonding them by means of diffusion bonding or brazing is generally used. As the metal thin plates used, copper plates are used because they have excellent thermal conductivity and easy machinability.

The copper has a thermal expansion coefficient, 17*10⁻⁶/k while a substrate of gallium arsenide that is generally used in a high-power semiconductor laser device has a thermal expansion coefficient, 5.9*10⁻⁶/k. This large difference in the thermal expansion coefficient causes a stress to occur when a semiconductor laser chip is fixed to a heat sink with solder and then they are cooled to the normal temperature.

It is known that, if turning on electricity through the semiconductor laser chip with any stress occurring in the chip, any crystalline defects accelerates in number thereof, thereby exerting a bad influence upon reliability of the laser.

In order to solve it, proposed has been a technology such that soft solder, for example, indium solder is used or a sub mount made of copper tungsten or the like, which has a thermal expansion coefficient approached to that of the semiconductor laser chip, is inserted into a position between the heat sink and the laser chip (see Japanese Patent Application Publication No. 2004-186527).

SUMMARY OF THE INVENTION

If the indium solder is used for bonding the semiconductor laser chip, the solder may show fragility due to alloyed indium solder when turning on electricity through the semiconductor laser chip for a long time and hence, reliability of the chip deteriorates. If the sub mount is inserted into the position between the heat sink and the chip, heat-removing efficiency decreases based on the thermal resistance in the sub mount.

Heat sink of micro channel type has a structure such that the higher heat-removing efficiency can be implemented by increasing a velocity of water flowing just under the chip. However, corrosion of the metal material may occur at this portion, thereby causing water to leak therefrom.

If semiconductor laser device is stack type one such that plural sets of water-cooled members are stacked, any corrosion occurs electrically due to any difference in potential of two adjacent heat sinks, thereby causing thickness of a part of the heat sink that is near the water channel to decrease and water to leak therefrom.

It is desirable to present a semiconductor laser device and a heat sink used therein that can prevent any stress from occurring without decreasing heat-removing efficiency.

According to an embodiment of the present invention, there is provided a semiconductor laser device having a heat sink of which laminated plural plates are constituted and a semiconductor laser element mounted on upper surface of the heat sink. The heat sink has a channel in which a coolant, for example, water flows inside thereof. The heat sink includes a channel-forming plate portion that forms the channel and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel. The mounting plate portion is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser element than that of the channel-forming plate portion.

According to another embodiment of the present invention, there is provided a heat sink of which laminated plural plates are constituted. The heat sink has a channel in which a coolant flows inside thereof. A surface of the heat sink mounts a semiconductor laser element. The heat sink includes a channel-forming plate portion that forms the channel and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel. The mounting plate portion is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser element than that of the channel-forming plate portion.

According to any embodiments of the invention, heat generated when driving the semiconductor laser element is transferred to the heat sink. The heat sink having a channel in which a coolant, for example, water, flows inside thereof removes the heat received from the semiconductor laser element. This allows the semiconductor laser element to be cooled.

In the heat sink, the mounting plate portion on which the semiconductor laser element is mounted is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser element than that of the channel-forming plate portion. This allows any stress generated in the semiconductor laser element to be reduced when expanding and contracting the semiconductor laser element and the mounting plate portion based on the heat generated for driving the semiconductor laser element.

Thus, according to any embodiments of the invention, any stress generated in the semiconductor laser element can be reduced, and hence, reliability of the semiconductor laser element can be improved. Since a whole upper surface of the heat sink can be made of single species of material in the embodiment, it is possible to prevent heat-removing efficiency based on the thermal resistance from decreasing.

Since the mounting plate portion on which the semiconductor laser element is mounted is made of material, for example, insulating material, having a thermal expansion coefficient, which is nearer that of the semiconductor laser element, in the embodiment of the heat sink, it is possible to avoid any corrosion occurring on a part that contacts the channel to prevent water from leaking therefrom.

The concluding portion of this specification particularly points out and directly claims the subject matter of the present invention. However those skills in the art will best understand both the organization and method of operation of the invention, together with further advantages and objects thereof, by reading the remaining portions of the specification in view of the accompanying drawing(s) wherein like reference characters refer to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an embodiment of a semiconductor laser device according to the invention for illustrating a configuration thereof;

FIG. 2 is a sectional side elevation of the embodiment of the semiconductor laser device according to the invention for illustrating a configuration thereof;

FIG. 3 is a sectional side elevation of another embodiment of a semiconductor laser device according to the invention;

FIG. 4 is an exploded perspective view of an upper heat sink constituting another embodiment of the semiconductor laser device according to the invention; and

FIG. 5 is an exploded perspective view of a lower heat sink constituting another embodiment of the semiconductor laser device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe embodiments of semiconductor laser device and heat sink according to the invention with reference to the accompanying drawings.

(A Configuration of First Embodiment of Semiconductor Laser Device According to the Invention)

FIG. 1 is an exploded perspective view of a first embodiment of each of the semiconductor laser device and the heat sink used therein according to the invention for illustrating a configuration thereof. FIG. 2 is a sectional side elevation of the first embodiment of the semiconductor laser device according to the invention for illustrating a configuration thereof.

A first embodiment of the semiconductor laser device 1A contains a heat sink 2 having a fine channel structure of micro channel type and a semiconductor laser chip 3 mounted thereon. This embodiment of the heat sink 2 is constituted of laminated thin plates. In this embodiment, the heat sink 2 is constituted of the following plates as five layers: a laser-chip-mounting plate 4 as a first layer; radiation-fin-forming plates 5, 6 as second and fourth layers; and channel-forming plates 7, 8 as third and fifth layers. The plates are bonded together to each other using the diffusion bonding or the like to form the heat sink 2.

The laser-chip-mounting plate 4 is an example of the mounting plate portion. The laser-chip-mounting plate 4 is thin plate on which the semiconductor laser chip 3 is mounted. The laser-chip-mounting plate 4 is made of material having a thermal expansion coefficient, which is nearer that of material of the semiconductor laser chip 3. If the semiconductor laser chip 3 is made of substrate of gallium arsenide that is generally used, the laser-chip-mounting plate 4 is made of metallic material such as Kovar or copper-tungsten alloy or ceramics such as aluminum nitride or silicon carbide.

If the laser-chip-mounting plate 4 is made of ceramics that are an insulating material, a metal layer 4 m is formed on a surface thereof using rolled gold so that the metal layer 4 m and an electrode formed on a lower surface of the semiconductor laser chip 3 can be connected electrically.

The radiation-fin-forming plate 5 is an example of the channel-forming plate portion. The radiation-fin-forming plate 5 is made of, for example, material having higher thermal conductivity. The radiation-fin-forming plate 5 has a radiation-fin-forming channel 9 therein.

The radiation-fin-forming plate 6 is an example of the channel-forming plate portion. The radiation-fin-forming plate 6 is made of, for example, material having higher thermal conductivity, similar to a case of the radiation-fin-forming plate 5. The radiation-fin-forming plate 6 has a radiation-fin-forming channel 10, a coolant-supplying-channel-forming hall 11, and a coolant-discharging-channel-forming hall 12 therein. In this case, if the laser-chip-mounting plate 4 is made of ceramics, the radiation-fin-forming plates 5, 6 are made of copper or the like that has excellent thermal conductivity and is capable of diffusion-bonding to the ceramics.

The radiation-fin-forming channel 9 is formed in the radiation-fin-forming plate 5 so that it passes through the radiation-fin-forming plate 5 in a height direction thereof. Plural radiation fins 9 f that arranged as to be positioned under the semiconductor laser chip 3 are projected in a line toward the inside of the channel 9 and hence, a coolant flows in a space between the radiation fins 9 f in the radiation-fin-forming channel 9.

The radiation-fin-forming channel 10 is formed in the radiation-fin-forming plate 6 so that it passes through the radiation-fin-forming plate 6 in a height direction thereof. Plural radiation fins 10 f that arranged as to be positioned under the semiconductor laser chip 3 are projected in a line toward the inside of the channel 10 and hence, a coolant flows in a space between the radiation fins 10 f in the radiation-fin-forming channel 10. The radiation-fin-forming channel 10 elongates to form a coolant-supplying channel 10 i for supplying a coolant to the radiation fins 10 f.

The coolant-supplying-channel-forming hall 11 and the coolant-discharging-channel-forming hall 12 are respectively formed in the radiation-fin-forming plate 6 so that they pass through the radiation-fin-forming plate 6 in a height direction thereof. These halls 11, 12 are separately formed from the radiation-fin-forming channel 10 in the radiation-fin-forming plate 6.

The channel-forming plate 7 is an example of the channel-forming plate portion. The channel-forming plate 7 is made of same material as that of the laser-chip-mounting plate 4. The channel-forming plate 7 has a circulation channel 13, a coolant-supplying-channel-forming hall 14, and a coolant-discharging-channel-forming hall 15 therein.

The channel-forming plate 8 is an example of the channel-forming plate portion. The channel-forming plate 8 is made of same material as that of the laser-chip-mounting plate 4, similar to a case of the channel-forming plate 7. The channel-forming plate 8 has a coolant-supplying-channel-forming hall 16 and a coolant-discharging-channel-forming hall 17 therein. For example, if the laser-chip-mounting plate 4 is made of ceramics, the channel-forming plates 7, 8 are mode of ceramics.

The circulation channel 13 is formed in the channel-forming plate 7 so that it passes through the channel-forming plate 7 in a height direction thereof. The circulation channel 13 is formed so that it can be communicated to the radiation-fin-forming channel 9 in the radiation-fin-forming plate 5 and the radiation-fin-forming channel 10 in the radiation-fin-forming plate 6.

The coolant-supplying-channel-forming hall 14 is formed in the channel-forming plate 7 so that it passes through the channel-forming plate 7 in a height direction thereof. The coolant-supplying-channel-forming hall 14 is formed relative to its position and shape so that it can be communicated to the coolant-supplying-channel-forming hall 11 in the radiation-fin-forming plate 6 and the coolant-supplying channel 10 i.

The coolant-discharging-channel-forming hall 15 is formed in the channel-forming plate 7 so that it passes through the channel-forming plate 7 in a height direction thereof. The coolant-discharging-channel-forming hall 15 is formed relative to its position and shape so that it can be communicated to the radiation-fin-forming channel 9 in the radiation-fin-forming plate 5 and the coolant-discharging-channel-forming hall 12 in the radiation-fin-forming plate 6.

The coolant-supplying-channel-forming hall 16 is formed in the channel-forming plate 8 so that it passes through the channel-forming plate 8 in a height direction thereof. The coolant-supplying-channel-forming hall 16 is formed so that it can be communicated to the coolant-supplying-channel-forming hall 11 in the radiation-fin-forming plate 6. The coolant-discharging-channel-forming hall 17 is formed in the channel-forming plate 8 so that it passes through the channel-forming plate 8 in a height direction thereof. The coolant-discharging-channel-forming hall 17 is formed so that it can be communicated to the coolant-discharging-channel-forming hall 12 in the radiation-fin-forming plate 6.

To form the heat sink 2, the laser-chip-mounting plate 4, the radiation-fin-forming plate 5, the channel-forming plate 7, the radiation-fin-forming plate 6, and the channel-forming plate 8 are bonded together to each other using any diffusion bonding with the respective plates being stacked in turn.

This enables the radiation-fin-forming channel 9 in the radiation-fin-forming plate 5 and the radiation-fin-forming channel 10 in the radiation-fin-forming plate 6 to be communicated to each other through the circulation channel 13 in the channel-forming plate 7. This also enables the coolant-discharging-channel-forming hall 15 in the channel-forming plate 7, the coolant-discharging-channel-forming hall 12 in the radiation-fin-forming plate 6, and the coolant-discharging-channel-forming hall 17 in the channel-forming plate 8 to be communicated to each other to form a discharging channel 18. The discharging channel 18 is communicated to the radiation-fin-forming channel 9 in the radiation-fin-forming plate 5.

This further enables the coolant-supplying-channel-forming hall 14 in the channel-forming plate 7, the coolant-supplying-channel-forming hall 11 in the radiation-fin-forming plate 6, and the coolant-supplying-channel-forming hall 16 in the channel-forming plate 8 to be communicated to each other to form a supplying channel 19. The supplying channel 19 is communicated to the coolant-supplying channel 10 i of the radiation-fin-forming channel 10 in the radiation-fin-forming plate 6.

Thus, in the heat sink 2, formed is a channel 20 for a coolant in which the supplying channel 19 is communicated to the discharging channel 18 via the radiation-fin-forming channel 10 in the radiation-fin-forming plate 6, the circulation channel 13 in the channel-forming plate 7, and the radiation-fin-forming channel 9 in the radiation-fin-forming plate 5.

Since the heat sink 2 have five-layer-structure as described above, the laser-chip-mounting plate 4 as the first layer, the highest layer, the channel-forming plate 7, as the third layer, the middle layer, and the channel-forming plate 8 as the fifth layer, the lowest layer are made of one and the same material. The radiation-fin-forming plate 5 as the second layer and the radiation-fin-forming plate 6 as the fourth layer are made of one and the same material. This allows the heat sink to have a configuration that is symmetrical in a laminated direction thereof.

Thus, even when the temperature of the plates return to the normal temperature after they have been diffusion-bonded at high temperature, it is difficult for the heat sink 2 to be bent due to any differences in the thermal expansion coefficients of the laser-chip-mounting plate 4 as the first layer, the channel-forming plates 7, 8 as the third and fifth layers, and the radiation-fin-forming plates 5, 6 as the second and fourth layers.

The semiconductor laser chip 3 is an example of the semiconductor laser element. The semiconductor laser chip 3 has an array structure such that plural light-emitting parts are arranged in line. The laser-chip-mounting plate 4 of the heat sink 2 mounts the semiconductor laser chip 3 with solder.

When the laser-chip-mounting plate 4 is mode of ceramics, the metal layer 4 m is formed on an upper surface of the laser-chip-mounting plate 4 as described above. The metal layer 4 m is electrically connected to the electrodes, which are not shown, provided on the undersurface of the semiconductor laser chip 3. Electrodes provided on an upper surface of the semiconductor laser chip 3, which are not shown, and the metal layer 4 m are respectively connected to any separate driver devices, which is not shown, electrically by bonding wires or the like.

The semiconductor laser chip 3 mounted on the laser-chip-mounting plate 4 is positioned upper the plural radiation fins 9 f formed in the radiation-fin-forming plate 5 and the plural radiation fins 10 f formed in the radiation-fin-forming plate 6.

Since the laser-chip-mounting plate 4 of the heat sink 2 is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser chip 3, as described above, the laser-chip-mounting plate 4 and the semiconductor laser chip 3 is made almost identical in a rate of expansion and contraction by heat. This prevents any stress from occurring in the semiconductor laser chip 3 when the heat sink 2 bonds the semiconductor laser chip 3 with solid solder such as alloy of gold and tin.

Thus, according to this embodiment, the heat sink 2 can bond the semiconductor laser chip 3 with solid solder such as alloy of gold and tin, thereby avoiding any deterioration in the solder even if electricity flows for long time. This enables the semiconductor laser device to maintain reliability for long time.

(Operations of the First Embodiment of the Semiconductor Laser Device According to the Invention)

The following will describe operations of the first embodiment of the semiconductor laser device 1A.

In the semiconductor laser device 1A, the supplying channel and the discharging channel 18 are connected to a circulation device, which is not shown, for supplying and discharging a coolant, so-called “chiller”.

In the heat sink 2, when the supplying channel 19 receives the coolant, the coolant flows through the channel 20 in which the supplying channel 19 is communicated to the discharging channel 18 via the radiation-fin-forming channel 10 in the radiation-fin-forming plate 6, the circulation channel 13 in the channel-forming plate 7, and the radiation-fin-forming channel 9 in the radiation-fin-forming plate 5.

Thus, the coolant received by the supplying channel 19 flows through the coolant-supplying channel 10 i in the radiation-fin-forming plate 6 to the radiation-fin-forming channel 10. In the radiation-fin-forming channel 10, the coolant flows in a space between the radiation fins 10 f to the radiation-fin-forming channel 9 in the radiation-fin-forming plate 5 via the circulation channel 13 in the channel-forming plate 7. In the radiation-fin-forming channel 9, the coolant flows in a space between the radiation fins 9 f to the discharging channel 18 from which the coolant is discharged.

The semiconductor laser chip 3 receives an electric signal from the driver device, which is not shown, and converts it to an optical signal to output it. Any heat occurring at driving the semiconductor laser chip 3 is transferred to the heat sink 2 through the laser-chip-mounting plate 4. Since the coolant flows in the channel 20 of the heat sink 2, as described above, the heat transferred from the semiconductor laser chip 3 can be removed. This enables the semiconductor laser chip 3 to be cooled.

In the heat sink 2 of this embodiment, the radiation fins 9 f, 10 f are positioned under the mounted position of the semiconductor laser chip 3. The radiation fins 9 f, 10 f can enlarge areas for contacting the coolant. The radiation fins 9 f, 10 f can generate any turbulent flows. This enables any heat transferred from the semiconductor laser chip 3 to be efficiently removed.

Since the coolant flows fast under the semiconductor laser chip 3 in the heat sink 2 of micro channel type, it is possible to implement higher heat-removing efficiency because fast-flown coolant is contacted to the undersurface of the laser-chip-mounting plate 4 on which the semiconductor laser chip 3 is mounted.

In this embodiment, the laser-chip-mounting plate 4 on which the semiconductor laser chip 3 is mounted and the undersurface of which contacts the coolant is made of ceramics as well as the channel-forming plates 7, 8 are made of ceramics. This prevents alteration in thickness of the metal material by corrosion thereof from occurring at the portion to which fast-flown coolant is contacted and prohibits water from being leaked therefrom.

Further, since in this embodiment, the radiation-fin-forming plates 5, 6 are made of metallic material that has good thermal conductivity such as copper, it is possible to enhance heat-removing efficiency. If the radiation-fin-forming plates 5, 6 are further provided with a suitable corrosion proof region, the whole of the heat sink 2 can prevent the coolant from leaking.

In this embodiment, the laser-chip-mounting plate 4 on which the semiconductor laser chip 3 is mounted is made of ceramics as well as the channel-forming plate 7 provided between the radiation-fin-forming plates 5, 6 and the channel-forming plate 8 provided under the radiation-fin-forming plate 6 are made of ceramics. This configuration prohibits current for driving the semiconductor laser chip 3 from flowing in the radiation-fin-forming plates 5, 6 made of metallic material. This prevents stray current corrosion by any potential difference due to internal resistance from occurring.

In the heat sink 2 of this embodiment, it is possible to bond the semiconductor laser chip 3 to the upper surface of the heat sink 2 directly with solid solder. This enables thermal resistance and electric resistance to decrease in contrast with a case where any sub mount made of another material is inserted into a mounted position of the semiconductor laser chip 3.

In this embodiment, the laser-chip-mounting plate 4 constituting upper surface of the heat sink 2 has relatively low thermal conductivity in contrast with copper or the like of which the radiation-fin-forming plates 5, 6 are made. If the laser-chip-mounting plate 4 made of the same material and having the same thickness as the laser-chip-mounting plate 4 when using the sub mount is used, it is possible to decrease at least the total of thermal resistance in contrast with a case when using the sub mount is used.

(A Configuration of Second Embodiment of Semiconductor Laser Device According to the Invention)

FIG. 3 is a sectional side elevation of a second embodiment of a semiconductor laser device according to the invention for illustrating a configuration thereof.

This semiconductor laser device 1B in the second embodiment is a semiconductor laser device of so-called stack type in which, for example, two semiconductor laser devices 1A in the first embodiment are stacked in a vertical direction thereof.

It is to be noted that although two semiconductor laser devices have been stacked in this embodiment, this invention is not limited to this. For example, twenty semiconductor laser devices can be stacked, thereby implementing any high-power semiconductor laser device.

Such the semiconductor laser device 1B in this embodiment has an upper heat sink 2A and a lower heat sink 2B each having a fine channel structure of micro channel type. Each of the heat sinks 2A, 2B mounts the semiconductor laser chip 3.

FIG. 4 is an exploded perspective view of the second embodiment of the upper heat sink 2A according to the invention for illustrating a configuration of the important portion thereof.

The upper heat sink 2A has the same configuration as that of the first embodiment of the heat sink 2 shown in FIG. 1 and is constituted of laminated thin plates. In this embodiment, the upper heat sink 2A is constituted of the following plates as five layers: a laser-chip-mounting plate 4A as a first layer; radiation-fin-forming plates 5A, 6A as second and fourth layers; and channel-forming plates 7A, 8A as third and fifth layers. The plates are bonded together to each other using the diffusion bonding or the like to form the upper heat sink 2A.

The laser-chip-mounting plate 4A is made of material, for example, ceramics having a thermal expansion coefficient, which is nearer that of material of the semiconductor laser chip 3A. If the laser-chip-mounting plate 4A is made of ceramics that are an insulating material, a metal layer 4Am is formed on a surface thereof using rolled gold so that the metal layer 4Am and electrodes formed on a lower surface of the semiconductor laser chip 3A can be connected electrically to each other.

The radiation-fin-forming plates 5A and 6A are made of material having higher thermal conductivity, for example, copper. The radiation-fin-forming plate 5A has a radiation-fin-forming channel 9A therein. The radiation-fin-forming plate 6A has a radiation-fin-forming channel 10A, a coolant-supplying-channel-forming hall 11A, and a coolant-discharging-channel-forming hall 12A therein. In this case, the radiation-fin-forming channel 9A, the radiation-fin-forming channel 10A, the coolant-supplying-channel-forming hall 11A, and the coolant-discharging-channel-forming hall 12A are formed in the respective plates similar to those of the first embodiment of the heat sink 2 shown in FIG. 1.

The channel-forming plates 7A, 8A are made of same material as that of the laser-chip-mounting plate 4A. The channel-forming plate 7A has a circulation channel 13A, a coolant-supplying-channel-forming hall 14A, and a coolant-discharging-channel-forming hall 15A therein. The channel-forming plate 8A has a coolant-supplying-channel-forming hall 16A and a coolant-discharging-channel-forming hall 17A therein. In this case, the circulation channel 13A, the coolant-supplying-channel-forming hall 14A, the coolant-discharging-channel-forming hall 15A, the coolant-supplying-channel-forming hall 16A and the coolant-discharging-channel-forming hall 17A are formed in the respective plates similar to those of the first embodiment of the heat sink 2 shown in FIG. 1.

In the upper heat sink 2A, the laser-chip-mounting plate 4A mounts the semiconductor laser chip 3A with solder. A spacer plate 21 is bonded on the laser-chip-mounting plate 4A on a portion thereof except for a portion where the semiconductor laser chip 3A is mounted. The spacer plate 21 is made of the same material, for example, ceramics, as that of the laser-chip-mounting plate 4A. A metal layer 21 m is formed on an upper surface of the spacer plate 21 using rolled gold or the like.

When the laser-chip-mounting plate 4A is mode of ceramics, the metal layer 4Am is formed on an upper surface of the laser-chip-mounting plate 4A as described above. The metal layer 4Am is electrically connected to the electrodes, which are not shown, provided on the undersurface of the semiconductor laser chip 3A. Electrodes provided on an upper surface of the semiconductor laser chip 3A, which are not shown, and the metal layer 21 m are connected electrically by bonding wires 22.

FIG. 5 is an exploded perspective view of the second embodiment of the lower heat sink 2 b according to the invention for illustrating a configuration of the important portion thereof.

The lower heat sink 2B has the same configuration as that of the first embodiment of the heat sink 2 except for a connection part thereof to the upper heat sink 2A and is constituted of laminated thin plates.

In this embodiment, the lower heat sink 2B is constituted of the following plates as five layers: a laser-chip-mounting plate 4B as a first layer; radiation-fin-forming plates 5B, 6B as second and fourth layers; and channel-forming plates 7B, 8B as third and fifth layers. The plates are bonded together to each other using the diffusion bonding or the like to form the lower heat sink 2B.

The laser-chip-mounting plate 4B is made of material, for example, ceramics having a thermal expansion coefficient, which is nearer that of material of the semiconductor laser chip 3B. The laser-chip-mounting plate 4B has a coolant-supplying-channel-forming hall 23 and a coolant-discharging-channel-forming hall 24 therein.

The coolant-supplying-channel-forming hall 23 and the coolant-discharging-channel-forming hall 24 are formed in the laser-chip-mounting plate 4B so that they pass through the laser-chip-mounting plate 4B in a height direction thereof. The coolant-supplying-channel-forming hall 23 is positioned so that it can be communicated to the coolant-supplying-channel-forming hall 16A of the upper heat sink 2A. The coolant-discharging-channel-forming hall 24 is positioned so that it can be communicated to the coolant-discharging-channel-forming hall 17A of the upper heat sink 2A.

If the laser-chip-mounting plate 4B is made of ceramics that are an insulating material, a metal layer 4Bm is formed on a surface thereof using rolled gold so that the metal layer 4 m and electrodes formed on a lower surface of the semiconductor laser chip 3B can be connected electrically to each other. It is to be noted that the coolant-supplying-channel-forming hall 23 and the coolant-discharging-channel-forming hall 24 are formed so that they pass through the metal layer 4Bm.

The radiation-fin-forming plates 5B, 6B are made of material having higher thermal conductivity, for example, copper. The radiation-fin-forming plate 5B has a radiation-fin-forming channel 9B and a coolant-supplying-channel-forming hall 25 therein. The radiation-fin-forming plate 6B has a radiation-fin-forming channel 10B, a coolant-supplying-channel-forming hall 11B, and a coolant-discharging-channel-forming hall 12B therein.

The radiation-fin-forming channel 9B is formed in the radiation-fin-forming plate 5B so that it passes through the radiation-fin-forming plate 5B in a height direction thereof. Plural radiation fins 9 f that arranged as to be positioned under the semiconductor laser chip 3B are projected in a line toward the inside of the channel 9B and hence, the coolant flows in a space between the radiation fins 9 f in the radiation-fin-forming channel 9B. The radiation-fin-forming channel 9B is positioned so that it can be communicated to the coolant-discharging-channel-forming hall 24 in the laser-chip-mounting plate 4B.

The radiation-fin-forming channel 10B is formed in the radiation-fin-forming plate 6B so that it passes through the radiation-fin-forming plate 6B in a height direction thereof. Plural radiation fins 10 f that arranged as to be positioned under the semiconductor laser chip 3 are projected in a line toward the inside of the channel 10B and hence, the coolant flows in a space between the radiation fins 10 f in the radiation-fin-forming channel 10B. The radiation-fin-forming channel 10B elongates to form a coolant-supplying channel 10 i for supplying a coolant to the radiating fins 10 f.

The coolant-supplying-channel-forming hall 11B and the coolant-discharging-channel-forming hall 12B are respectively formed in the radiation-fin-forming plate 6B so that they pass through the radiation-fin-forming plate 6B in a height direction thereof. These halls 11B, 12B are separately formed from the radiation-fin-forming channel 10B in the radiation-fin-forming plate 6B.

The channel-forming plates 7, 8 are made of same material, for example, ceramics, as that of the laser-chip-mounting plate 4B. The channel-forming plate 7B has a circulation channel 13B, a coolant-supplying-channel-forming hall 14B, and a coolant-discharging-channel-forming hall 15B therein. The channel-forming plate 8B has a coolant-supplying-channel-forming hall 16B and a coolant-discharging-channel-forming hall 17B therein.

The circulation channel 13B is formed in the channel-forming plate 7B so that it passes through the channel-forming plate 7B in a height direction thereof. The circulation channel 13B is formed so that it can be communicated to the radiation-fin-forming channel 9B in the radiation-fin-forming plate 5B and the radiation-fin-forming channel 10B in the radiation-fin-forming plate 6B.

The coolant-supplying-channel-forming hall 14B is formed in the channel-forming plate 7B so that it passes through the channel-forming plate 7B in a height direction thereof. The coolant-supplying-channel-forming hall 14B is formed relative to its position and shape so that it can be communicated to the coolant-supplying-channel-forming hall 25 in the radiation-fin-forming plate 5B, the coolant-supplying-channel-forming hall 11B in the radiation-fin-forming plate 6B, and the coolant-supplying channel 10 i.

The coolant-discharging-channel-forming hall 15B is formed in the channel-forming plate 7B so that it passes through the channel-forming plate 7B in a height direction thereof. The coolant-discharging-channel-forming hall 15B is formed relative to its position and shape so that it can be communicated to the radiation-fin-forming channel 9B in the radiation-fin-forming plate 5B and the coolant-discharging-channel-forming hall 12B in the radiation-fin-forming plate 6B.

The coolant-supplying-channel-forming hall 16B is formed in the channel-forming plate 8B so that it passes through the channel-forming plate 8B in a height direction thereof. The coolant-supplying-channel-forming hall 16B is formed so that it can be communicated to the coolant-supplying-channel-forming hall 11B in the radiation-fin-forming plate 6B. The coolant-discharging-channel-forming hall 17B is formed in the channel-forming plate 8B so that it passes through the channel-forming plate 8B in a height direction thereof. The coolant-discharging-channel-forming hall 17B is formed so that it can be communicated to the coolant-discharging-channel-forming hall 12 b in the radiation-fin-forming plate 6B.

In the lower heat sink 2B, if the laser-chip-mounting plate 4B on which the semiconductor laser chip 3B is mounted is made of ceramics and the channel-forming plates 7B, 8B are made of ceramics to make the heat sink have a configuration that is symmetrical in a laminated direction thereof, the radiation-fin-forming plates 5B, 6B are made of material having excellent thermal conductivity, for example, copper that is diffusion-bonded to the ceramics.

In the lower heat sink 2B, the laser-chip-mounting plate 4B mounts the semiconductor laser chip 3B with solder or the like. A spacer plate 26 is bonded on the laser-chip-mounting plate 4B on a portion thereof except for a portion where the semiconductor laser chip 3B is mounted. The spacer plate 26 is made of the same material, for example, ceramics, as that of the laser-chip-mounting plate 4B. A metal layer 26 m is formed on an upper surface of the spacer plate 26 using rolled gold or the like.

The spacer plate 26 has a coolant-supplying-channel-forming hall 27 and a coolant-discharging-channel-forming hall 28 therein. The coolant-supplying-channel-forming hall 27 is formed in a position so that it can be communicated to the coolant-supplying-channel-forming hall 23 in the laser-chip-mounting plate 4B. The coolant-discharging-channel-forming hall 28 is formed in a position so that it can be communicated to the coolant-discharging-channel-forming hall 24 in the laser-chip-mounting plate 4B.

When the laser-chip-mounting plate 4B is mode of ceramics, the metal layer 4Bm is formed on an upper surface of the laser-chip-mounting plate 4B as described above. The metal layer 4Bm is electrically connected to the electrodes, which are not shown, provided on the undersurface of the semiconductor laser chip 3B. Electrodes provided on an upper surface of the semiconductor laser chip 3B, which are not shown, and the metal layer 26 m are connected electrically by bonding wires 29.

To form the upper heat sink 2A, the laser-chip-mounting plate 4A, the radiation-fin-forming plate 5A, the channel-forming plate 7A, the radiation-fin-forming plate 6A, and the channel-forming plate 8A are bonded together to each other using any diffusion bonding with the respective plates being stacked in turn. In the upper heat sink 2A, the spacer plate 21 is bonded to the laser-chip-mounting plate 4A.

This enables the radiation-fin-forming channel 9A in the radiation-fin-forming plate 5A and the radiation-fin-forming channel 10A in the radiation-fin-forming plate 6A to be communicated to each other through the circulation channel 13A in the channel-forming plate 7A in the upper heat sink 2A. This also enables the coolant-discharging-channel-forming hall 15A in the channel-forming plate 7A, the coolant-discharging-channel-forming hall 12A in the radiation-fin-forming plate 6A, and the coolant-discharging-channel-forming hall 17A in the channel-forming plate 8A to be communicated to each other to form a discharging channel 18A. The discharging channel 18A is communicated to the radiation-fin-forming channel 9A in the radiation-fin-forming plate 5A.

This further enables the coolant-supplying-channel-forming hall 14A in the channel-forming plate 7A, the coolant-supplying-channel-forming hall 11A in the radiation-fin-forming plate 6A, and the coolant-supplying-channel-forming hall 16A in the channel-forming plate 8A to be communicated to each other to form a supplying channel 19A. The supplying channel 19A is communicated to the coolant-supplying channel 10 i of the radiation-fin-forming channel 10A in the radiation-fin-forming plate 6A.

To form the lower heat sink 2B, the laser-chip-mounting plate 4B, the radiation-fin-forming plate 5B, the channel-forming plate 7B, the radiation-fin-forming plate 6B, and the channel-forming plate 8B are bonded together to each other using any diffusion bonding with the respective plates being stacked in turn. In the lower heat sink 2B, the spacer plate 26 is bonded to the laser-chip-mounting plate 4B.

This enables the radiation-fin-forming channel 9B in the radiation-fin-forming plate 5B and the radiation-fin-forming channel 10B in the radiation-fin-forming plate 6B to be communicated to each other through the circulation channel 13B in the channel-forming plate 7B in the lower heat sink 2B.

This also enables the coolant-discharging-channel-forming hall 28 in the spacer plate 26, the coolant-discharging-channel-forming hall 24 in the laser-chip-mounting plate 4B, the radiation-fin-forming channel 9B in the radiation-fin-forming plate 5B, the coolant-discharging-channel-forming hall 15B in the channel-forming plate 7B, the coolant-discharging-channel-forming hall 12B in the radiation-fin-forming plate 6B, and the coolant-discharging-channel-forming hall 17B in the channel-forming plate 8B to be communicated to each other to form a discharging channel 18B.

This further enables the coolant-supplying-channel-forming hall 27 in the spacer plate 26, the coolant-supplying-channel-forming hall 23 in the laser-chip-mounting plate 4B, the coolant-supplying-channel-forming hall 25 in the radiation-fin-forming plate 5B, the coolant-supplying-channel-forming hall 14B in the channel-forming plate 7B, the coolant-supplying-channel-forming hall 11B in the radiation-fin-forming plate 6B, and the coolant-supplying-channel-forming hall 16B in the channel-forming plate 8B to be communicated to each other to form a supplying channel 19B. The supplying channel 19B is communicated to the radiation-fin-forming channel 10B in the radiation-fin-forming plate 6B via the coolant-supplying-channel-forming hall 14B in the channel-forming plate 7B and the coolant-supplying channel 10 i of the radiation-fin-forming plate 6B.

Thus, the upper heat sink 2A and the lower heat sink 2B are boned with the discharging channels 18A, 18B and the supplying channels 19A, 19B being sealed by O-ring 30. This enables the upper heat sink 2A and the lower heat sink 2B to be communicated to each other, thereby forming a channel 31.

Since the upper heat sink 2A have five-layer-structure as described above, the laser-chip-mounting plate 4A as the first layer, the highest layer thereof, the channel-forming plate 7A as the third layer, the middle layer thereof, and the channel-forming plate 8A as the fifth layer, the lowest layer thereof are made of one and the same material. The radiation-fin-forming plate 5A as the second layer and the radiation-fin-forming plate 6A as the fourth layer are made of one and the same material. This allows the heat sink 2A to have a configuration that is symmetrical in a laminated direction thereof.

Since the lower heat sink 2B have five-layer-structure as described above, the laser-chip-mounting plate 4B as the first layer, the highest layer thereof, the channel-forming plate 7B as the third layer, the middle layer thereof, and the channel-forming plate 8B as the fifth layer, the lowest layer thereof are made of one and the same material. The radiation-fin-forming plate 5B as the second layer and the radiation-fin-forming plate 6B as the fourth layer are made of one and the same material. This allows the lower heat sink 2B to have a configuration that is symmetrical in a laminated direction thereof.

Thus, even when the temperature of the plates return to the normal temperature after they have been diffusion-bonded at high temperature, it is difficult for the upper and lower heat sinks 2A, 2B to be bent due to any differences in the thermal expansion coefficients of the respective plates constituting the layers.

Relative to electric connection of the semiconductor laser chip 3 in the semiconductor laser device 1B, in the upper heat sink 2A, the metal layer 21 m of the spacer plate 21 that is connected to the upper electrodes, which is not shown, of the semiconductor laser chip 3A is connected to the power supply of the driver device 32 or the like. In the lower heat sink 2B, the metal layer 4Bm of the laser-chip-mounting plate 4B that is connected to the lower electrodes, which is not shown, of the semiconductor laser chip 3B is also connected to the power supply of the driver device 32 or the like.

Further, the metal layer 4Am of the laser-chip-mounting plate 4A that is connected to the lower electrodes, which is not shown, of the semiconductor laser chip 3A in the upper heat sink 2A and the metal layer 26 m of the spacer plate 26 that is connected to the upper electrodes, which is not shown, of the semiconductor laser chip 3B in the lower heat sink 2B are connected to each other by bonding wires 33.

This enables electric current to flow in the upper and lower semiconductor laser chips 3A, 3B in series from the driver device 32.

The laser-chip-mounting plate 4A of the upper heat sink 2A is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser chip 3A. This prevents any stress from occurring in the semiconductor laser chip 3A when the upper heat sink 2A bonds the semiconductor laser chip 3A with solid solder such as alloy of gold and tin. Thus, according to this embodiment, it is possible to avoid any deterioration in the solder even if electricity flows for long time. This enables the semiconductor laser device to maintain reliability for long time.

Similarly, the laser-chip-mounting plate 4B of the lower heat sink 2B is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser chip 3B. This prevents any stress from occurring in the semiconductor laser chip 3B when the lower heat sink 2B bonds the semiconductor laser chip 3B with solid solder such as alloy of gold and tin. Thus, according to this embodiment, it is possible to avoid any deterioration in the solder even if electricity flows for long time. This enables the semiconductor laser device to maintain reliability for long time.

(Operations of the Second Embodiment of the Semiconductor Laser Device According to the Invention)

The following will describe operations of the second embodiment of the semiconductor laser device 1B.

In the semiconductor laser device 1B, the supplying channel 19B and the discharging channel 18B in the lower heat sink 2B are connected to a circulation device, which is not shown, for supplying and discharging a coolant.

In the lower heat sink 2B, when the supplying channel 19B receives the coolant, a portion of the coolant flows toward the radiation-fin-forming channel 10B in the radiation-fin-forming plate 6B via the coolant-supplying channel 10 i therein. In the radiation-fin-forming channel 10B, the coolant flows in a space between the radiation fins 10 f to the radiation-fin-forming channel 9B in the radiation-fin-forming plate 5B via the circulation channel 13B in the channel-forming plate 7B. In the radiation-fin-forming channel 9B, the coolant flows in a space between the radiation fins 9 f to the discharging channel 18B from which the coolant is discharged.

When the supplying channel 19B receives the coolant, the other portion of the coolant passes through the supplying channel 19B to reach the supplying channel 19A in the upper heat sink 2A. When the supplying channel 19A receives the coolant, this portion of the coolant flows toward the radiation-fin-forming channel 10A in the radiation-fin-forming plate 6A via the coolant-supplying channel 10 i therein. In the radiation-fin-forming channel 10A, the coolant flows in a space between the radiation fins 10 f to the radiation-fin-forming channel 9A in the radiation-fin-forming plate 5A via the circulation channel 13A in the channel-forming plate 7A. In the radiation-fin-forming channel 9A, the coolant flows in a space between the radiation fins 9 f from the discharging channel 18A to the discharging channel 18A of the lower heat sink 2B from which the coolant is discharged.

Each of the semiconductor laser chips 3A, 3B receives an electric signal from the driver device 32 and converts it to an optical signal to output it. It is to be noted that a lens, which is not shown, condenses the optical signal irradiated from any of the semiconductor laser chips 3A, 3B to make incident on an optical fiber, for example, thereby obtaining an optical signal with high-power.

Any heat occurring at driving the semiconductor laser chip 3A is transferred to the upper heat sink 2A through the laser-chip-mounting plate 4A. Since the coolant flows in the channel 31, as described above, in the upper heat sink 2A, the heat transferred from the semiconductor laser chip 3A can be removed. This enables the semiconductor laser chip 3A to be cooled.

Similarly, any heat occurring at driving the semiconductor laser chip 3B is almost transferred to the lower heat sink 2B through the laser-chip-mounting plate 4B. Since the coolant flows in the channel 31, as described above, in the lower heat sink 2B, the heat transferred from the semiconductor laser chip 3B can be removed. This enables the semiconductor laser chip 3B to be cooled.

In this embodiment, the coolant flows fast under the semiconductor laser chips 3A and/or 3B in the upper and lower heat sinks 2A, 2B of micro channel type and hence, it is possible to implement higher heat-removing efficiency.

In the upper heat sink 2A, the laser-chip-mounting plate 4A on which the semiconductor laser chip 3A is mounted and the undersurface of which contacts the coolant is made of ceramics as well as the channel-forming plates 7A, 8A are made of ceramics. This prevents alteration in thickness of the metal material by corrosion thereof from occurring at the portion to which fast-flown coolant is contacted and prohibits water from being leaked therefrom.

Further, in this embodiment, the radiation-fin-forming plates 5A, 6A are made of metallic material that has good thermal conductivity such as copper, and hence, it is possible to enhance heat-removing efficiency. If the radiation-fin-forming plates 5A, 6A are further provided with a suitable corrosion proof region, the whole of the upper heat sink 2A can prevent the coolant from leaking.

In the lower heat sink 2B, similar to a case of the upper heat sink 2A, the laser-chip-mounting plate 4B on which the semiconductor laser chip 3B is mounted and the undersurface of which contacts the coolant is made of ceramics as well as the channel-forming plates 7B, 8B are made of ceramics. This prevents alteration in thickness of the metal material by corrosion thereof from occurring at the portion to which fast-flown coolant is contacted and prohibits water from being leaked therefrom.

Further, in this embodiment, the radiation-fin-forming plates 5B, 6B are made of metallic material that has good thermal conductivity such as copper, and hence, it is possible to enhance heat-removing efficiency. If the radiation-fin-forming plates 5B, 6B are further provided with a suitable corrosion proof region, the whole of the lower heat sink 2B can prevent the coolant from leaking.

The upper heat sink 2A and the lower heat sink 2B are boned with the discharging channels 18A, 18B and the supplying channels 19A, 19B being sealed by O-ring 30. This may prevent the coolant from being leaked out of the whole of heat sink.

In the upper heat sink 2A, the laser-chip-mounting plate 4A on which the semiconductor laser chip 3A is mounted is made of ceramics that are insulating material and the metal layer 4Am on the laser-chip-mounting plate 4A is electrically connected to the semiconductor laser chip 3A. The channel-forming plate 7A provided between the radiation-fin-forming plates 5A, 6A and the channel-forming plate 8A provided under the radiation-fin-forming plate 6A are made of ceramics that are insulating material. This configuration prohibits current for driving the semiconductor laser chip 3A from flowing in the radiation-fin-forming plates 5A, 6A made of metallic material.

Similarly, in the lower heat sink 2B, the laser-chip-mounting plate 4B on which the semiconductor laser chip 3B is mounted is made of ceramics that are insulating material and the metal layer 4Bm on the laser-chip-mounting plate 4B is electrically connected to the semiconductor laser chip 3B. The channel-forming plate 7B provided between the radiation-fin-forming plates 5B, 6B and the channel-forming plate 8B provided under the radiation-fin-forming plate 6B are made of ceramics that are insulating material. This configuration prohibits current for driving the semiconductor laser chip 3B from flowing in the radiation-fin-forming plates 5B, 6B made of metallic material.

This enables electric potential of each of the radiation-fin-forming plates 5A, 6A of the upper heat sink 2A and the radiation-fin-forming plates 5B, 6B of the upper heat sink 2A is separated from that of each of the semiconductor laser chips 3A, 3B and fixed by the supplied coolant. This allows the respective radiation-fin-forming plates made of metallic material that is contacted with the coolant to become equipotential, thereby preventing electric corrosion due to any potential difference between the upper and lower heat sinks from occurring.

Thus, in this embodiment, it is possible to prevent the electric corrosion from occurring at the metallic plates without purifying the coolant, thereby managing the coolant easily, in contrast with a post case where the coolant, water is purified and electric conductivity is decreased, thereby preventing the electric corrosion by potential difference of the upper and lower heat sinks from occurring.

In this embodiment, if the laser-chip-mounting plates 4A, 4B are made of ceramics and power is supplied to each of the semiconductor laser chips 3A, 3B through the metal layers 4Am, 4Bm provided on the laser-chip-mounting plates 4A, 4B, large amount of current can flow in such the thin metal layers 4Am, 4Bm, so that operation voltage of the semiconductor laser device is increased based on a voltage drop due to it.

If so, in this embodiment, the metal layers 4Am, 4Bm are made using rolled gold and thus, thickness thereof is increased so that no voltage drop may occur. Further, in this embodiment, the laser-chip-mounting plates 4A, 4B, and the channel-forming plates 7A, 8A, 7B, 8B can be made of ceramics and a metal layer can be formed on side surfaces of the upper and lower heat sinks 2A, 2B so that they can be connected to each other.

Additionally, any via hole can be provided in the upper and lower heat sinks 2A, 2B and hence, the upper and lower heat sinks 2A, 2B can be communicated to each other. If so, the radiation-fin-forming plates 5A, 5B, 6A, 6B that are contacted with the coolant become equipotential with the semiconductor laser chips 3A, 3B, thereby generating any potential difference between the upper and lower heat sinks 2A, 2B. If so, this embodiment prevents alteration in thickness of the metal material by corrosion thereof from occurring at the portion to which fast-flown coolant is contacted and prohibits water from being leaked therefrom when the laser-chip-mounting plates 4A, 4B are made of ceramics.

Still further, in this embodiment, the laser-chip-mounting plates 4A, 4B can be made of metallic material to have electric conductivity. If so, the laser-chip-mounting plate 4A, 4B and the channel-forming plates 7A, 7B, 8A, 8B are made of material having higher electropositive potential than those of the radiation-fin-forming plates 5A, 5B, 6A, 6B. Since the laser-chip-mounting plate 4A, 4B can be made of metallic material, the radiation-fin-forming plates 5A, 5B, 6A, 6B that are contacted with the coolant become equipotential with the semiconductor laser chips 3A, 3B, thereby generating any potential difference between the upper and lower heat sinks 2A, 2B. In this embodiment, however, the laser-chip-mounting plates 4A, 4B are made of material having higher electropositive potential than those of the radiation-fin-forming plates 5A, 5B, 6A, 6B, so that the radiation-fin-forming plates 5A, 5B, 6A, 6B can become sacrifice electrodes, thereby preventing any corrosion from occurring at the lower portions of the laser-chip-mounting plates 4A, 4B to which fast-flown coolant is connected. In this case, inner sides of the radiation-fin-forming plates 5A, 5B, 6A, 6B can be eaten. If so, in this embodiment, the channel has longer than that of a case where the heat sink is made of metal only and hence, the portions of radiation-fin-forming plates 5A, 5B, 6A, 6B that are connected with the channels become longer so that resistance of the radiation-fin-forming plates 5A, 5B, 6A, 6B is increased to make current decreased, thereby enabling a degree of corrosion in the radiation-fin-forming plates 5A, 5B, 6A, 6B and the like to be reduced.

It is preferable to apply these embodiments to a high-power semiconductor laser device that is used for processing a welding, a disconnecting or the like.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 

1. A semiconductor laser device comprising: a heat sink of which laminated plural plates are constituted, said heat sink having inside thereof a channel in which a coolant flows; and a semiconductor laser element mounted on upper surface of the heat sink, wherein the heat sink includes a channel-forming plate portion that forms the channel and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel; and wherein the mounting plate portion is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser element than that of the channel-forming plate portion.
 2. The semiconductor laser device according to claim 1, wherein the channel-forming plate portion is made of material having higher thermal conductivity than that of the mounting plate portion.
 3. The semiconductor laser device according to claim 1, wherein the channel-forming plate portion includes plural plates; wherein in the heat sink, a part of the channel-forming plate portion is made of same material as that of the mounting plate portion; and wherein the heat sink has a configuration that is symmetrical in a laminated direction thereof.
 4. The semiconductor laser device according to claim 1, wherein the mounting plate portion is made of ceramics that are an insulating material.
 5. The semiconductor laser device according to claim 4, wherein the channel-forming plate portion is made of copper that is diffusion-bonded to the ceramics.
 6. The semiconductor laser device according to claim 4, wherein a metal layer is formed on a surface of the mounting plate portion that is insulated to the channel-forming plate portion, to connect the metal layer and the semiconductor laser element electrically.
 7. The semiconductor laser device according to claim 1, wherein the mounting plate portion is made of metallic material selected from a group of Kovar and copper-tungsten alloy.
 8. The semiconductor laser device according to claim 1, wherein plural sets of the heat sinks are stacked and the mounting plate portion of each of the heat sinks mounts the semiconductor laser element.
 9. The semiconductor laser device according to claim 8, wherein the channel-forming plate portion includes plural plates; and wherein in the heat sink, a lower surface of the mounting plate portion and at least one of the plates in the channel-forming plate portion are made of insulating material to make other plate in the channel-forming plate portion separate from electric potential of the semiconductor laser element.
 10. The semiconductor laser device according to claim 8, wherein the channel-forming plate portion includes plural plates; and wherein in the heat sink, a lower surface of the mounting plate portion and at least one of plates in the channel-forming plate portion are made of material having higher electropositive potential than that of other plate in the channel-forming plate portion.
 11. A heat sink of which laminated plural plates are constituted, said heat sink having inside thereof a channel in which a coolant flows, a surface of the heat sink mounting a semiconductor laser element, and the heat sink including: a channel-forming plate portion that forms the channel; and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel, wherein the mounting plate portion is made of material having a thermal expansion coefficient, which is nearer that of the semiconductor laser element than that of the channel-forming plate portion.
 12. The heat sink according to claim 11, wherein the mounting plate portion is made of ceramics that are an insulating material.
 13. The heat sink according to claim 12, wherein the channel-forming plate portion has a higher thermal conductivity than that of the mounting plate portion and is made of metal material that is diffusion-bonded to the ceramics.
 14. The heat sink according to claim 11, wherein the channel-forming plate portion includes plural plates; wherein a part of the channel-forming plate portion is made of same material as that of the mounting plate portion; and wherein the heat sink has a configuration that is symmetrical in a laminated direction thereof. 